The present invention relates to an apparatus for measuring the intensity of ultrasonic waves in a cleaning tank, and more particularly to an apparatus for precisely measuring the intensity of ultrasonic waves according to the relative position within the cleaning tank.
A shadow mask is generally cleaned during the manufacture of a cathode ray tube by placement into a cleaning tank where the vibrations of ultrasonic waves clean the mask.
FIG. 1 shows the structure of a conventional ultrasonic wave cleaning tank in which a diaphragm 11 including a plurality of vibrators 12 is installed near the bottom of the cleaning tank 10 where the diaphragm 11 vibrates according to the vibrations of the vibrators 12 to generate ultrasonic waves.
FIG. 2 shows a phase of the ultrasonic wave generated by the vibration of diaphragm 11. That is, the ultrasonic waves generated from the diaphragm 11 of a sound source are reflected on a water surface 20 according to characteristics of the vibrators 12 (see FIG. 1), and takes the form of a standing wave including a peak 21 and a node 22. However, the intensity of the ultrasonic waves is maximum at the peak 21 and minimum at the node 22. Accordingly, an object to be cleaned (not shown) in the cleaning tank 10 of FIG. 1 is cleaned effectively at the peak 21 of the wave, but ineffectively at the node 22. The poor-cleaning regions have a detrimental influence on the reliability of cleaning the mask. Accordingly, it is important to precisely measure the positions of each peak 21 and each node 22. The position of the peak 21 and the node 22 can be known by measuring the intensity of the ultrasonic waves in the vertical direction with respect to the water surface.
Also, the characteristics of each vibrator 12 may differ. Accordingly, the intensity of each ultrasonic wave may be different on the same plane parallel to the water surface 20. However, it is not easy to precisely measure the intensity of each ultrasonic wave according to each position.
The conventional intensity of the ultrasonic waves in the cleaning tank has been calculated according to mathematical and physical theories. That is, the distance between the diaphragm of the sound source and the water surface has been measured and the intensity of the ultrasonic waves has been calculated according to a standing wave theory based on the measured distance. However, the result of the calculation is theoretical so that the actual intensity of the ultrasonic waves is not precisely indicated.
One method for measuring the actual intensity of the ultrasonic waves is to place a piece of aluminum foil into the cleaning tank and then generate ultrasonic waves to observe the cleaning of the aluminum foil and thereby measure the intensity of the ultrasonic waves. That is, in a portion of the aluminum foil where the intensity of the ultrasonic waves is high, fine holes or wear in the foil can be observed, and in a portion of the aluminum foil where the intensity thereof is low, there is virtually no change.
However, with the above method, the position of the aluminum foil cannot be precisely set, so that the intensity of the ultrasonic waves cannot be precisely measured at each position. Also, the distribution of intensities with respect to each position in the cleaning tank cannot be understood by measurement thereof with a piece of aluminum foil.